Tin Mössbauer spectroscopy of tin-rich iridium-tin alloys

Ir₅Sn₇, Ir₃Sn₇ and newly obtained IrSn₄ /4/ exhibit complex Mössbauer spectra. The positions of the individual lines range from 0.82 to 3.0 mm/s and the average isomer shift \(\overline {IS} \) derived for each compound of Sn atomic percentage x follows the relationship: \(\overline {IS} = 0.60 + 0.0194 x\) . Rather large quadrupole splittings are obtained. The f factors are about 0.20 at 295 K and 0.37 at 78 K, from which Debye temperatures of 200 to 300 K have been calculated.     

Mössbauer spectroscopy study of the disordering process of Fe-rich FeAlSi alloys

In this work we study systematically the influence of different Al/Si ratios on the magnetic and structural properties of mechanically disordered powder Fe₇₅Al_25?x Si _x , Fe₇₀Al_30?x Si _x and Fe₆₀Al_40?x Si _x alloys by means of Mössbauer spectroscopy and X-ray diffraction measurements. In order to obtain different stages of disorder the alloys were deformed by ball milling annealed (ordered) alloys during different number of hours. X-ray and Mössbauer data show that mechanical deformation induces the disordered A2 structure in these alloys. The results indicate that addition of Si to binary Fe–Al alloys makes the disordering more difficult. The study of the hyperfine fields indicates that depending on the Fe content the magnetic behaviour of these ternary alloys varies. For Fe₇₅Al_25?x Si _x series, the alloys have different magnetic behaviours with deformation depending on the Si content. The magnetization of the alloys with high Si content decreases with deformation, as it happens to binary Fe₇₅Si₂₅ and the magnetization of the alloys with low Si content increases with deformation, as it happens to binary Fe₇₅Al₂₅. For Fe₇₀Al_30?x Si _x series the mean hyperfine fields show that there are two different stages with the disordering, in a first stage the mean hyperfine fields decrease and in the second stage they increase. Finally, for Fe₆₀Al_40?x Si _x alloys there is a magnetic transition, from a paramagnetic ordered state to a magneticdisordered state.     

Mössbauer spectroscopy of 151 europium dicarboxylates

We have previously reported the stability of europium oxalate compared to ammonium europium bis-salen and europium benzoate. We now extend the dicoarboxylic acid chain of the oxalate by introducing additional-CH₂-groups in the dicarboxylate ligands by using malonate, succinate, glutarate and adipate. Additionally, we have examined the effect of alterations in the succinate dianion by introducing functional groups such as [C = C]in the case of the maleide and-OH group in the case of the malide. This study is an attempt to further characterize these compounds. Infrared spectra were used to characterize bridging and chelating dicarboxylates while Mössbauer spectroscopy measurements were used to gain better insight into the structure of heterocyclic “cages” containing two Eu^3?+? ions and two dianions.     

Practical aspects of Mössbauer spectroscopy instrumentation

The setting up and updating of a Mössbauer laboratory imply the acquisition and assembling of different units. Guidelines concerning either the construction or the acquisition of the various parts which compose a Mössbauer spectrometer are given in this paper.     

Mössbauer spectroscopy in catalysis

Application of in situ Mössbauer spectroscopy for studying catalysts and catalytic processes is discussed. Examples are presented to illustrate the potentials of the method by describing studies on supported heterogeneous catalysts performed with ¹¹⁹Sn and ⁵⁷Fe spectroscopies in cases with certain metals and alloys, oxides and porous substances. The results are interpreted in comparison to the catalytic performance.     

67Zn Mössbauer spectroscopy

The 93.31-keV Mössbauer resonance in⁶⁷Zn is used to determine tiny changes of the transition energy. We first report on a gravitational redshift (GRS) experiment with⁶⁷GaZnO single crystal source and⁶⁷ZnO powder as absorber. The results on the GRS show that solid state effects which are difficult to control experimentally, in particular the extreme sensitivity of the electric field gradient tensor (efg) in⁶⁷ZnO to small external pressure, finally limit the accuracy in determining the GRS. The resonance has been further employed to investigate solid state properties of⁶⁷ZnO with high precision. At large pressures⁶⁷ZnO exhibits a phase transition from hep (wurtzite) to fcc (NaCl) structure. The changes of the efg and of the s-electron density θ(0) at the⁶⁷Zn nucleus with reduced unit cell volume show that covalency of the Zn-O bond plays and essential role. We have performed self-consistent Hartree-Pock cluster calculations to describe the experimental changes of θ(0) in detail.     

Mössbauer spectroscopy at ISOLDE

Applications of radioactive ion beams produced at the ISOLDE facility for Mössbauer studies of probe atoms in solids are presented. Examples are given for a site-selective incorporation on different substitutional sites in compound semiconductors by ion implantation and thermal annealing of the radiation damage resulting from the implantation. The interactions of the probe atoms with lattice defects created in the implantation process have been studied to elucidate likely causes for the site-selective implantation mechanism. The technique has enabled to determine the electronic densities at electrically active substitutional probe atoms, having shallow donor or acceptor states as well as states deeper in the band gap. The results are in good agreement with theoretical results from local density calculations. Methodological aspects of the Mössbauer emission techniques employed at ISOLDE are compared to alternative accelerator based techniques and the consequences of the application of different precursor isotopes to the ⁵⁷Fe Mössbauer isotope are treated in detail for ⁵⁷Fe in silicon. Finally, results obtained for the magnetic hyperfine interactions of 5 sp impurities associated with vacancies in ferromagnetic metals are discussed.     

Development of 125Te synchrotron-radiation-based Mössbauer spectroscopy

The Mössbauer spectra of the 35.49 keV excited state of ¹²⁵Te were observed in the energy domain using synchrotron radiation for the first time. The obtained isomer shifts and Debye temperature agree with previous experiments. These results show that this method will be applicable to various compounds.     

Characterization of magnetic nano-fluids via Mössbauer spectroscopy

The laser pyrolysis became a useful tool, providing various ways, in production of nano materials. The iron Mössbauer spectroscopy is one very accurate method in evidencing the physical properties and related processes in the nano scale compounds. The effect of pressure, laser spot area and induced combustion, of gas mixture and laser power on the phase composition and inside particle distribution, grain size as well as the related phenomena were investigated by temperature dependent Mössbauer spectroscopy. A selection of most relevant properties is presented and discussed in details.     

Mössbauer spectroscopy of lanthanum and holmium ferrites

PrRh₂Si₂ is highly anisotropic Ising-type antiferromagnetic system. The ordering temperature (T _N~ 68 K) of PrRh₂Si₂ is exceptionally high on the de-Gennes scale in the family of RRh₂Si₂ (R = rare earths). The reason for this anomalous behaviour is not clear. It is believed that the presence of uniaxial anisotropy assists in enhancing the T _N. The Mössbauer study was performed on a 10% Fe-doped PrRh₂Si₂ sample to understand the magnetic coupling between different sites of PrRh₂Si₂. The Mössbauer spectra together with the magnetic susceptibility data suggest that the magnetic coupling in PrRh₂Si₂ is provided mainly by the RKKY interaction between Pr-moments.     

Mössbauer spectroscopy study of interfaces for spintronics

The submonolayer sensitivity and element-specificity of conversion electron Mössbauer spectroscopy, combined with the use of ⁵⁷Fe enriched tracer layers, enable to carefully investigate thin films and interfaces at the atomic-scale. This paper reports on the main achievements we obtained so far in the study of structural, chemical, and magnetic properties of a variety of interfaces between oxides and Fe-based films having potential interest in the field of spintronics.     

Mössbauer study of internally oxidized silver-tin alloys

A Mössbauer study of internally formed oxides as a function of oxidation temperatures between 200 C and 850 C was performed on previously annealed 1 at%AgSn alloys. The oxide formed at high temperatures (t 500 C) consists in agglomerates of tin dioxide = 0.00 ± 0.01 mm/s, Q=0.50 ± 0.03 mm/s). The low temperature oxide (t 300 C) is characterized by = 0.29 ± 0.02 mm/s and Q=0.32 ± 0.03 mm/s, and could be in the form of one-Sn-atom oxide complexes in the silver matrix. From the measured isomer shifts in the range 400 t 550 C, the maximum contribution of the silver matrix to the effective number of electrons per Sn atom in oxide agglomerates has been estimated have a value of about 0.06. The effect of the cold work on the hyperfine parameters of the oxidized tin has also been investigated. As rolled samples were found to attain the same values of isomer shifts and quadrupole splittings as annealed specimens, but at lower temperatures.     

Corrosion studies of iron and its alloys by means of57Fe Mössbauer spectroscopy

Some of the advantages and limitations of Mössbauer spectroscopy when used in corrosion research are shown by using three examples taken from the work of the authors on (i) the passive layer of iron, (ii) the corrosion of weathering steels by SO₂-polluted atmospheres and (iii) the performance of rust converters.     

Mössbauer spectroscopy in molecular magnetism

The aim of this paper is to highlight some selected research activities on molecular magnetic materials using Mössbauer spectroscopy as a technique carried out in our laboratory in recent years. The first part of the present article is devoted to the studies of the various magnetic interactions, metal-to-metal electron-transfer phenomenon, glass transition occurring in molecular magnetic materials, whereas the second part deals with the iron(II) high spin (S = 2)–low spin (S = 0) transition phenomenon occurring in some isoxazole ligand based iron(II) compounds as examples with unusually complicated spin transition behaviour. Also, an example of a dinuclear a spin crossover compound of iron(II) is described, where Mössbauer spectroscopy has most convincingly unraveled the mechanism of the spin transition process. Finally, an example from our most recent studies of spin crossover materials exhibiting both thermal spin crossover and liquid crystalline properties in the same temperature interval near room temperature will be presented.     

Fast detectors for Mössbauer spectroscopy

The methods to increase the productivity (statistical quality) of Mössbauer measurements have been considered. Some fast detectors for gamma- and secondary radiation have been described. These detectors allow in many cases to essentially reduce the time for the Mössbauer spectra accumulation with a given productivity.     

Mössbauer spectroscopy with actinide elements

Although formally equivalent to the lanthanide (4f) elements, the light actinides show a much more varied behaviour due to the larger spatial extent and ionizability of the 5f electrons. The application of Mössbauer spectroscopy for the determination of electronic properties of the actinides is outlined. Emphasis is put on high pressure Mössbauer experiments using the 60 keV transition in²³⁷Np to study questions of delocalization of 5f electrons.Work performed under the auspices of the Bundesministerium für Forschung und Technologie, Federal Republic of Germany.     

Mössbauer spectroscopy in physical metallurgy

In this anniversary contribution the natural and intimate match making which occurs between the two star performers-⁵⁷Fe in Mössbauer spectroscopy and iron in physical metallurgy—is described by selecting typical examples reflecting the author's interest: phases, f.c.c. -Fe, defects, diffusion and amorphous metals.     

Application of Mössbauer spectroscopy on corrosion products of NPP

Steam generator (SG) is generally one of the most important components at all nuclear power plants (NPP) with close impact to safe and long-term operation. Material degradation and corrosion/erosion processes are serious risks for long-term reliable operation. Steam generators of four VVER-440 units at nuclear power plants V-1 and V-2 in Jaslovske Bohunice (Slovakia) were gradually changed by new original “Bohunice” design in period 1994–1998, in order to improve corrosion resistance of SGs. Corrosion processes before and after these design and material changes in Bohunice secondary circuit were studied using Mössbauer spectroscopy during last 25 years. Innovations in the feed water pipeline design as well as material composition improvements were evaluated positively. Mössbauer spectroscopy studies of phase composition of corrosion products were performed on real specimens scrapped from water pipelines or in form of filters deposits. Newest results in our long-term corrosion study confirm good operational experiences and suitable chemical regimes (reduction environment) which results mostly in creation of magnetite (on the level 70 % or higher) and small portions of hematite, goethite or hydrooxides. Regular observation of corrosion/erosion processes is essential for keeping NPP operation on high safety level. The output from performed material analyses influences the optimisation of operating chemical regimes and it can be used in optimisation of regimes at decontamination and passivation of pipelines or secondary circuit components. It can be concluded that a longer passivation time leads more to magnetite fraction in the corrosion products composition.